A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simplified network architecture. LTE systems also provide seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of base stations, e.g., evolved Node-Bs (eNBs) communicating with a plurality of mobile stations referred as user equipments (UEs).
A Buffer status report (BSR) is sent from the UE to the serving eNB to provide information about the amount of pending data in the uplink buffer of the UE. The buffer status, along with other information, such as priorities allocated to different logical channels, is useful for the uplink scheduling process to determine which UEs or logical channels should be granted radio resources at a given time. The UE communicates the BSR to the scheduler in the base station so that the base station has sufficient information about the data waiting in the UE for UL transmission. The base station can allocate appropriate UL resource for the UE in a timely manner. Traditionally, the UE reports the buffer status to only one base station, which is its serving base station. This method encounters problem with the use of inter-base station carrier aggregation.
Carrier aggregation (CA) is introduced to improve system throughput. With carrier aggregation, the LTE-Advance system can support higher data rate. Such technology is attractive because it allows operators to aggregate several smaller contiguous or non-continuous component carriers (CC) to provide a larger system bandwidth, and provides backward compatibility by allowing legacy users to access the system by using one of the component carriers. LTE also allows carrier aggregation from different eNBs or from different radio access technology (RAT). Different from the traditional wireless system, with inter-eNB or inter-RAT carrier aggregation, the UE needs to associate with multiple schedulers from different base stations. For inter-BS carrier aggregation, the base stations providing the carrier components are not physically collocated, it requires transmission medium and interfaces among the base stations. Therefore, the UE has to provide separate BSRs to different schedulers residing in different base stations.
Improvements and enhancements are required for UE BSR procedures to communicate and manage multiple schedulers from different base stations.